This proposal continues the development and testing of a novel, safe, and effective treatment device for onychomycosis (nail fungal infection). Onychomycosis is a common infectious disease with potentially serious consequences. The infected nail is a persistent reservoir for microbes that can lead to significant medical problems including cellulitis, skin ulceration, and gangrene. Over 38 million Americans suffer from onychomycosis, which carries a direct cost of over $4 billion in the US healthcare system. Unlike current oral treatments that may cause liver damage, or topical creams and lasers that have low or unproven efficacy, the device under development in this grant offers patients and doctors a reliable, convenient method to treat nail fungal infections without toxic side effects. I this project, we will test our patent-pending technology on human patients to prove the clinical feasibility of treating fungal infections with our medical device prototype. Our critical success metric for this Phase II project is mycological cure (i.e., 100% fungal killing) and clear nail growth in onychomycosis patients. This is a necessary step to reduce technical risk in the ultimate development of an FDA-approved medical device for curing onychomycosis. In support of our product goal, we propose to answer four critical questions related to the utility of this novel device: 1)Do the three clinical instruments pass validations testing to show consistent and similar performance?; 2)Is the instrument functional in a clinical setting as related to user instructions, user interface and human factor analysis?; 3) Can performing a three treatment protocol over a week result in mycological cure for the patient?; 4) Will the treatment result in clear nail growth for the patient over a 6-month interval?